1. Field of the Invention
Apparatuses consistent with the present invention relate to a liquid crystal display having an improved viewing angle and brightness, and more particularly, to a liquid crystal display with a polarized light guide plate which has improved polarization separating performance and increases the amount of light illuminated along the normal direction to provide a wide viewing angle and a high brightness.
2. Description of the Related Art
A liquid crystal display is a non-emissive flat panel display device which requires an additional light source to form images, such as a backlight unit. Generally, a liquid crystal display has low light efficiency. The liquid crystal display converts or preserves the polarization of linearly polarized light transmitted through liquid crystals, to transmit or block the light based on the arrangement of the liquid crystals. The liquid crystal display uses only light that is linearly polarized in one direction, and thus polarization plates are formed on both sides of the liquid crystal display. These are absorptive polarization plates that transmit light polarized in one direction and absorb light polarized in another direction. Since the absorptive polarization plates absorb about 50% of the incident light, they are the greatest cause of the low light efficiency of the liquid crystal display.
Examples of operation modes for liquid crystals to form images in a liquid crystal display include a twisted nematic (TN) mode, an in-plane switching (IPS) mode, and a vertical alignment (VA) mode. The TN mode is easy and inexpensive to manufacture, and thus is frequently used in mobile phones or laptop computers. However, the TN mode causes the contrast ratio to change and the gray scale to reverse based on the viewing angle. These phenomena are due to the 90° twisted structure of TN cells. In other words, when the light from the illumination system is linearly polarized by the polarization plates and then transmitted through optically anisotropic liquid crystals, the phase of the light varies based on the angle at which the light passes through the liquid crystals. For example, the phase delay degree of the light varies when the light passes through the liquid crystals vertically and when the light passes through the liquid crystals at an angle, thereby generating a phase difference.
FIG. 1 is a schematic view of a related art liquid crystal display 30. Referring to FIG. 1, the liquid crystal display 30 includes a light source 26, a light guide plate 32, an optical path controlling layer 34, a liquid crystal panel 14, and a diffusion plate 16. Light 22 passing the light guide plate 32 at an angle of θ1 with respect to a vertical line N is collimated in a distribution range of about ±10° with respect to light 23 having an angle of θ2 with respect to the vertical line N while passing the optical path controlling layer 34, and is then incident on the liquid crystal panel 14. An image formed on the liquid crystal panel 14 passes through the diffusion plate 16 and thus has a wider viewing angle. Although the liquid crystal display has an improved viewing angle, the maximum front brightness is not achieved. Also, because the liquid crystal display has a structure in which unpolarized light is incident on the liquid crystal panel, the light efficiency is low and the front brightness is limited.